The present invention relates to lubricating oil compositions and in particular to lubricating oil compositions suitable for medium or low speed diesel engines, such as marine diesel engines, including the four-stroke trunk-piston engine.
Lubricating oils for such engines are known and typically contain a range of additives which will perform a variety of functions. However contamination of these lubricating oil compositions with unburned residual fuel oil is a problem recognized in the industry. This leads to severe engine cleanliness problems in service which is sometimes referred to as “black paint” of asphaltene deposits. The problem is particularly widespread in marine diesel engines, such as 4-stroke trunk-piston engines where dirty cam boxes and crankcases are encountered, and 2-stroke cross-head engines which usually use two separate lubricating oils, one for the crankcase and one for the cylinder. It is in the crankcase of these 2-stroke engines where there is potential for these heavy deposits to occur.
There is a need for lubricating compositions that address the asphaltene and/or “black paint” deposit issues, such as those seen in marine diesel engines without reducing the lubricating compositions performance in other areas, including overall detergency.